Ramadan water-fasting and builders etc.

I read a few years ago that water drinking was something most Muslims were supposed to abstain from during Ramadan.

I think this is ok, to some extent, and there are exemptions from this rule, but what about people whose job involves heavy physical work, especially in what might be hot weather?

On a course I did for carpentry the tutor said he used to be a roofer, and he had to drink quite a bit, during hot days..multiple gallons, I think he said, and he said he didn't even need to go for a pee, which suggests he really did need the hydration.

How can builders, farmers etc, really not drink water though a long day, whilst Ramadan is in the summer months?